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Terrible Time for Toads

Populations are declining in some Western states, but not others; ISU scientists work to learn why

Boreal toad populations have declined severely in Colorado, but not in western Wyoming or Montana. Idaho State University researchers are trying to learn why.

Researchers in the College of Arts and Sciences Department of Biological Sciences are tracking these nocturnal animals by using tiny radio transmitters that are attached to the amphibians. The transmitters enable researchers to record the toads' movements, temperature and habitat use.

Scientists say the die-offs of the southern boreal toads appear to have been caused by a fungal skin disease, the same disease that has caused dieoff s of amphibians worldwide.

ISU researchers are working under a grant from the United States Geological Survey and National Park Service with colleagues from these agencies and the Colorado Division of Wildlife. The team includes Murphy and fellow ISU biological sciences professors Sophie St.-Hilaire, Ph.D., DVM, and Charles Peterson, Ph.D.

Murphy says it is unknown why the fungus causes death. "We know that in Grand Teton boreal toads, more than 50 percent carry the pathogen (the fungus), but there are no recent die-offs."

Die-offs of the southern populations of the boreal toad (Bufo boreas boreas), including those from southeast Wyoming, Colorado and New Mexico, have been so severe that they were considered for listing and protection under the federal Endangered Species Act (ESA).

The toad has not been observed in New Mexico since 1986, according to Peter Murphy, Ph.D., Idaho State University visiting biology professor.

Southern populations of the toad were not considered sufficiently distinct from the northern, and were denied ESA listing in 2005. They are listed as "state endangered" by the Colorado Division of Wildlife.

Tracking toads in the field isn't easy in the mountains of Wyoming and Colorado. Research sites are located in and near Grand Teton National Park, and in the Bears Ears Mountains of Colorado near Steamboat Springs.

Among several hypotheses, the ISU researchers suggest that, because the habitat of toads is at higher elevation in Colorado than in Wyoming, there is a smaller window of opportunity each day in Colorado for toads to achieve high body temperatures and knock back the growth of the fungus. So it may achieve lethal levels more often.

Andy Taylor
ISU Magazine